While we use a big share with 10+ users, I personally didn't get many conflicts during the Nextcloud installation's lifetime. I got a couple of "You changed this in two computers, and I need to sync both" states, and it duplicated the files with appending the hostname or something else useful. At the end, I either merged them myself or thought "meh, this copy is not needed anymore, anyway" and deleted one of them.
If other users got any conflicts, and got anything borked, I'd have known, since I'm the admin of the installation. However I can't guarantee anything. I think it's working reasonably well for other people, too.
It has some mitigation strategies, and has a pretty extensive list of transient files (like Microsoft Word lock files), so everything works pretty straightforward for us.
It's creating far less problems than I expected, though.
